1. Field of the Invention
The present invention relates to a lapping apparatus and a lapping method for film-lapping (hereinafter simply called “lapping”) a pre-machined surface of a work by a lapping film (hereinafter simply and occasionally called “film”) provided with abrasive grains.
2. Description of the Related Art
There has been recently conducted lapping by a lapping film having one surface provided with abrasive grains, in case of finishing a work having a cross-sectionally arcuate outer peripheral surface, such as pin portions and journal portions of a crankshaft or cam-lobe portions and journal portions of a camshaft.
Such lapping is conducted by covering a pre-machined surface of a work by a lapping film, and by machining the work by an abrasive-grained surface of the film while rotating the work in a state where the film is pressed from its back surface by a shoe toward the work. In addition to a mechanism for pressing a shoe toward a work via film, lapping apparatus has a mechanism for rotationally driving the work, and an oscillation mechanism for applying oscillation in an axial direction of the work to at least one of the work and lapping film (see FIG. 1 and FIG. 2 of Japanese Patent Application Laid-Open No. 7-237116).
Works include one having a pre-machined surface formed with an open holed portion. For example, pin portions and journal portions of a crankshaft are formed with lubricant holes as holed portions penetrating the crankshaft in a direction perpendicular to the axial direction of the crankshaft, respectively. Such lubricant holes are to preferably have mouth-base edges in cross-sectionally rounded shapes, respectively, so as not to damage the engaged components (such as bearing metal).
Thus, mouth-base edges of lubricant holes have been conventionally formed with rounded portions, by conducting additional machining for pressing abrasive-grained surfaces of lapping films to mouth bases of lubricant holes of a work by so-called soft shoes, after once lapping the work by pressing abrasive-grained surfaces of lapping films to the pre-machined surfaces of the work by so-called hard shoes, respectively.